Re: [PATCH v4 09/20] powerpc: Enable compile-time check for syscall handlers

From: "Nicholas Piggin" <npiggin@gmail.com>
To: "Rohan McLure" <rmclure@linux.ibm.com>, <linuxppc-dev@lists.ozlabs.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v4 09/20] powerpc: Enable compile-time check for syscall handlers
Date: Mon, 12 Sep 2022 20:42:32 +1000	[thread overview]
Message-ID: <CMUCZC1TQBYV.T5VOLUARFB7C@bobo> (raw)
In-Reply-To: <20220824020548.62625-10-rmclure@linux.ibm.com>

On Wed Aug 24, 2022 at 12:05 PM AEST, Rohan McLure wrote:
> The table of syscall handlers and registered compatibility syscall
> handlers has in past been produced using assembly, with function
> references resolved at link time. This moves link-time errors to
> compile-time, by rewriting systbl.S in C, and including the
> linux/syscalls.h, linux/compat.h and asm/syscalls.h headers for
> prototypes.

Well this is pretty cool.

Unrelated, but since commit ab66dcc76d6a, is
arch/powerpc/kernel/systbl_chk.sh unused in the tree?

>
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
> ---
> V1 -> V2: New patch.
> ---
>  arch/powerpc/kernel/{systbl.S => systbl.c} | 27 ++++++++++----------
>  1 file changed, 14 insertions(+), 13 deletions(-)
>
> diff --git a/arch/powerpc/kernel/systbl.S b/arch/powerpc/kernel/systbl.c
> similarity index 59%
> rename from arch/powerpc/kernel/systbl.S
> rename to arch/powerpc/kernel/systbl.c
> index cb3358886203..99ffdfef6b9c 100644
> --- a/arch/powerpc/kernel/systbl.S
> +++ b/arch/powerpc/kernel/systbl.c
> @@ -10,31 +10,32 @@
>   * PPC64 updates by Dave Engebretsen (engebret@us.ibm.com) 
>   */
>  
> -#include <asm/ppc_asm.h>
> +#include <linux/syscalls.h>
> +#include <linux/compat.h>
> +#include <asm/unistd.h>
> +#include <asm/syscalls.h>
>  
> -.section .rodata,"a"
> +#define __SYSCALL_WITH_COMPAT(nr, entry, compat) __SYSCALL(nr, entry)
>  
> -#ifdef CONFIG_PPC64
> -	.p2align	3
> -#define __SYSCALL(nr, entry)	.8byte entry
> +#ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
> +#define __SYSCALL(nr, entry) [nr] = __powerpc_##entry,
> +#define __powerpc_sys_ni_syscall	sys_ni_syscall
>  #else
> -#define __SYSCALL(nr, entry)	.long entry
> +#define __SYSCALL(nr, entry) [nr] = entry,
>  #endif
>  
> -#define __SYSCALL_WITH_COMPAT(nr, native, compat)	__SYSCALL(nr, native)
> -.globl sys_call_table
> -sys_call_table:
> +void *sys_call_table[] = {

Humour me, the asm version had this in rodata, does this change that or
does it somehow get put back in there? Should this be const?

Otherwise, 

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

>  #ifdef CONFIG_PPC64
>  #include <asm/syscall_table_64.h>
>  #else
>  #include <asm/syscall_table_32.h>
>  #endif
> +};
>  
>  #ifdef CONFIG_COMPAT
>  #undef __SYSCALL_WITH_COMPAT
>  #define __SYSCALL_WITH_COMPAT(nr, native, compat)	__SYSCALL(nr, compat)
> -.globl compat_sys_call_table
> -compat_sys_call_table:
> -#define compat_sys_sigsuspend	sys_sigsuspend
> +void *compat_sys_call_table[] = {
>  #include <asm/syscall_table_32.h>
> -#endif
> +};
> +#endif /* CONFIG_COMPAT */
> -- 
> 2.34.1